782 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [64] 



They may be described briefly as follows : 



Var. a. — Apical disk nearly or quite entire. Of this variety there 

 were two specimens; one adult with ripe segments, and which, while 

 living, measures 530 mm in length, diameters of anterior disk 3 and 3.5 mm 

 respectively; another, a young specimen, measuring in alcohol 40 mm in 

 length, diameters of anterior disk 2.1 and 2.2 mm respectively. 



Var. fi. — Apical disk large, with profound lateral notch. Of this va- 

 riety there were two specimens which did not differ much in size. One 

 of them while living measured 75 mm in length, diameters of anterior 

 disc 4.5 and 5 mm respectively. 



The following measurements of the adult specimen were obtained 

 while it was yet living : 



Miliuieters. 



Length of specimen 530.00 



Marginal diameter of disk 3.50 



Lateral diameter of disk 3.00 



Thickness of disk 1.25 



Diameter of cervical mass 2.00 



Breadth of nuseginented part of body 1.12 



Greatest breadth of body, 115 mm from bead 5.00 



Length of segments, 115 mm from head 1.00 



Length of posterior segments 2.45 



Breadth of posterior segments 3.25 



Longer diameter of ova 0.11 



Shorter diameter of ova 0.08 



The dimensions of the posterior segments are approximate, the seg- 

 ments themselves being quite variable. 



These parasites were found in July, 1886, attached to the mucous 

 membrane of the spiral valve of a dusky shark (Carcharias obscurus). 

 When found they were firmly attached, the flat anterior disk being en- 

 tirely embedded in the mucous membrane of the host. The only part 

 of the head that was visible was the yellow, globular, inflated mass, 

 behind the disk. When the worms were removed, which was effected, 

 in each case, with some difficulty, a flat pit with a narrow opening was 

 left in the mucous membrane. 



That part which I have interpreted as the head is a muscular, com- 

 pact, transversely flattened, terminal disk, which, in the adult and one 

 of the smaller specimens (var. cr), is slightly convex in front and con- 

 cave behind, with bluntly rounded entire edges. In the larger speci- 

 men there was a very faint indication of a lateral notch on the edge of 

 the disk. In these specimens there was no tendency to appress the 

 sides of the disk. The head, in fact, resembled in shape a cloth-covered 

 coat button, in which the disk represented the flat, exposed part of the 

 button and the inflated cervical mass that part of the button by which 

 it is fastened to the coat. In the alcoholic specimens the disk of var. a 

 is convex and yellowish-white above, flat and ashy gray below. On 

 the under side there are three or four radial slits, which are probably 

 cracks in the cuticle, due to the effect of the preservative. 



